Author Topic: Preventing Urinary Catheter Blockages  (Read 108 times)


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Preventing Urinary Catheter Blockages
« on: March 02, 2017, 04:44:59 AM »

According to the users' information leaflet, Nitrofurantoin (also known as Macrobid,  Macrodantin or Genfura) is used 1) to cure urinary infections and 2) to prevent them.  It is proved below that if used to prevent urinary infections, in my case it  also prevented catheter blockages.  I do not know for how many other people with catheter blockages it would be effective.  It would be unlikely to work for those who have blockages caused by kidney stones or bladder stones.
The normal dose for preventing urinary infections is 50 or 100mg daily at night.  Having taken 50mg per day for 30 days, this was reduced to 50mg 3 or 4 times per week and then to just nights when I was feeling feverish as might warn of a urinary infection or when there was a considerable amount of sediment in my catheter.  That worked for me, but others might need different doses.  Like other medications, Nitrofurantoin comes with many cautions and possible side-effects, listed in the users' information leaflet, but I have not had any at these doses.
As well as taking Nitrofurantoin I also repositioned my catheter by pulling it forward immediately after going to bed to prevent the intake being obstructed by pressing up against my bladder wall and, as far as possible, assisted drainage by gravity by placing my catheter flat on the bed rather than strapped to my leg.
I have also used several supporting methods to keep my catheter clear.  These are listed below.

From January to July 2016 the misery of my spinal injury was aggravated by the torment of catheter blockages.  Here are a few observations to help identify what had been causing them:
1    My suprapubic catheter was installed in May 2013, about 4 months after my spinal injury. I had no blockage during the first two years and eight months but I had 23 between 17/1/16 and 24/7/16.  Towards the end of that period, they became more frequent.
2     All the blockages occurred soon after changing positions from sitting upright in my wheelchair to lying flat on my back in bed.  On every occasion I have wakened up sweating and trembling with exceptionally violent spasms, usually between midnight and 1am.  There is a highly significant relationship between time and occurrence of blockages.  If we use  simple dichotomy that blockages could occur at either day or night, if there were no relationship between time of blockage and occurrence, the probability of any one blockage occurring at night would be 0.5.  The probability of all 23 blockages occurring at night would be 0.5 to the power 23 = 0.000000119 or a little over 1 chance in ten million.
The base is 0.5 and the exponent is 23.
The binomial distribution can also be used with the same result:

where N = 23, k = 23, p =0.5 and the answer is p(k out of N)

The multinomial can be used too:
where the number of outcomes is 2 (night/day), the number of occurrences 23 and 0, p = 0.5 for each outcome.
Sitting is a wheelchair, my catheter is usually strapped to the upper side of my left leg.  If left there when lying flat in bed, this part of my catheter might be at a higher level than the intake, impeding flow by gravity.  I have noticed that sweating has on a few occasions been stopped by unstrapping my catheter from my leg and laying it at a lower level on the bed.  Now I always have it unstrapped when in bed. 
3    The nurse has never taken more than a few minutes to unblock the obstruction.   It takes about 10 minutes for the sweating and spasms to subside enough to be clearly noticeable and a further 10 minutes for the sweating to have gone and the spasms returned to their normal level.  In perhaps 8 or 10 of my 23 cases of blockage, it was uncertain why the blockage had cleared.  Sometimes there was insufficient sediment for that to be a likely cause.  Movement of the catheter in some cases seemed to be sufficient to make the urine to flow.  Unblocking the catheter did not in every case cause a sudden, clearly visible flow of urine. 
4    Only once has a blockage recurred during the same night.  On this occasion, two nurses arrived at 10.50pm and replaced my catheter which was choked with 'sludge'.  At 2.40am I woke sweating again.  The same nurses returned.  This time the blockage was 'positional'.
5     There were at least two causes of the blockages - bacterial and physical obstruction.
6    For about half of the blockages, the nurse mentioned sediment and/or 'pus' as the likely cause.  On some occasions, including the most recent, only 36 hours after a bladder wash-out, the nurse said there was no sediment.
7    My leg bag is supposed to be changed weekly.  On 3 or 4 occasions, the nurse has mentioned a dirty leg bag, when the carers (and me) had forgotten about it or when we had run out of them.
8    On the morning following several of the blockages I have had a bout of sweating which has always been stopped by taking Nitrofurantoin.  This seems to indicate that I had a urinary infection, and that the infection was caused by bacteria which also caused the blockage the night before.  A urine sample has never been taken at the time of a blockage or soon after.  However, it seems likely that the bacteria killed by Nitrofurantoin created the sediment which resulted in most of the blockages. 
I do not have a good explanation as to why I had no blockages between installation of my catheter in May 2013 and 17/1/16 despite having more than a dozen urinary infections during this period.   I can only state the obvious that whatever bacteria were causing these infections did not produce sufficient sediment to cause a blockage but there was a change in January 2016.  Before July 2016 I took Nitrofurantoin only occasionally to cure urinary infections.
When Nitrofurantoin stopped my blockages it also removed the additional spasms accompanying the infection and the blockage.  So Nitrofurantoin achieve four results for me: i) it cured urinary infections;  ii) it prevented urinary infections; iii) it prevented blockages; iv) it cured/prevented additional spasms resulting from infections and blockages.
9    Weekly bladder wash-outs were started soon after the blockages began.  I have never had a blockage on the following night, but I have had them soon after. 
10    For about half the blockages, the nurse mentioned a physical obstruction, such as a collapsed tube.  I do not know why physical obstructions were absent from May 2013 until January 2016.  Maybe there was a change in type or brand of catheter in December 2015 or January 2016?
11    For the most recent blockage, the nurse offered the following explanation: the end of the catheter tube might be pressing up against my bladder wall, so obstructing the intake.  This fits well with what two or three other nurses have said:  'I'm not sure what caused the blockage but wiggling the catheter where it enters the bladder seemed to unblock it'.

AN  INITIAL  TRIAL:  15th JULY - 12th AUGUST 2016
From 17/1/16 to 24/7/16 I had 23 blockages, including 6 from 15 - 24/7/16.  It seemed that infections by bacteria were responsible for the majority of the blockages (point 8 above) and the position of my catheter for the others (point 11).   It is likely that some blockages were caused by a combination of the two: a constriction not severe enough to block the flow of urine caused sediment to collect on the upstream side and this caused a blockage.
So it is very likely that changing positions from wheelchair to bed triggered nearly all the blockages, most of which were caused by sediment in the catheter.  Why might changing positions cause an accumulation of sediment in my catheter?  Gravity would probably act more weakly in bed; sediment in my bladder might change position on going to bed and obstruct the intake of my catheter.  These are possible explanations as to why changing positions from wheelchair to lying flat in bed seemed to trigger blockages but I do not have a convincing answer.
Since 24/7/16  I have taken 50mg Nitrofurantoin each day at about 8pm to allow time for it to take effect before moving from wheelchair to bed (point 8) and pulled my catheter forward away from the bladder wall immediately after going to bed (point 11).  From 24/7/16 - 12/8/16 I had no blockage in 20 nights.

So WITHOUT Nitrofurantoin and catheter repositioning: 10 nights, 6 blockages;
WITH Nitrofurantoin and catheter repositioning: 20 nights, no blockage.

It looks obvious that there is a connection between Nitrofurantion/catheter repositioning and stopping blockages.  The strength of the evidence can be measured like this:
what are the chances of having 6 blockages on the first 10 nights (without Nitrofurantoin) and none on the following 20 (with Nitrofurantoin) if Nitrofurantoin and catheter repositioning had no effect?
That can be calculated like this:
if there had been just one blockage, the chances of it being in the first 10 nights would have been 10 divided by the total number of nights (30) =  0.3333;
if there had been two blockages the chances of both of them being in the first 10 nights would have been 0.3333 multiplied by 0.3333 = 0.1111 and so on   ......  until
the chances of 6 blockages all being in the first 10 nights is 0.3333 multiplied by itself five times or 0.33336 = 0.0014, that is 14 chances in 10,000 or 1 chance in 714 (10,000 is the number that 0.0014 would have to be multiplied by to get 14).  So the probability of there being no association between taking Nitrofurantoin/catheter repositioning is low, therefore the probability that there is an association is high.  It is 1 - p = 0.9986  = 9,986 chances in 10,000 = 9,986/(10,000 - 9,986) chances in 10,000/(10,000-9,986) = 713 chances in 714.

The probability of there being no association between taking Nitrofurantoin/catheter repositioning and the occurrence of catheter blockages can also be calculated using the binomial distribution where the probability of success for a single trial is again 10/30 = 0.3333, the number of trials is 6 (the number of blockages on all 30 nights) and the number of successes (hardly the right word for a catheter blockage - the number of blockages during the first 10 nights) is also 6.
The probability just calculated is 'if there is no association between Nitrofurantoin and catheter blockages, what are the chances of getting 6 blockages in the 10 nights without Nitrofurantoin?'  It can also be calculated the other way round: what are the chances of there being no blockage in 20 nights with Nitrofurantoin if lack of blockages is not associated with it?  In this case, the probability of success for a single trial is 20/30 = 0.6667 the number of trials is 6 (the number of blockages on all 30 nights) and the number of successes (the number of blockages on the last 20 nights) is 0.  The answer is the same, that is, probability = 0.0014.

The multinomial distribution can also be used with 2 outcomes (blockage/ no blockage) probability of outcome 1 (blockage) is 10/30 = 0.3333; frequency of outcome 1 (number of blockages when not taking Nitrofurantoin) = 6; probability of outcome 2 (no blockage) is 20/30 = 0.6667; frequency of outcome 2 is 0 (the number of blockages when taking Nitrofurantoin).  The answer is the same as before (p = 0.0014).

This too can be calculated the other way round: outcome 1 (no blockage, probability 0.6667, frequency 0); outcome 2 (blockage, probability 0.3333, frequency 6) with the same result.

So for the 30 nights of the trial, it is possible to say that taking Nitrofurantoin and catheter repositioning were associated with stopping my catheter blockages with only a very small chance of being wrong (probability 0.0014) which is 1 chance in 714. 
That was the situation on 13/8/16.  It is changing every day.  If I have a blockage, the chances of the statement being wrong will increase.  If I do not have a blockage, the chances of the statement being wrong will become even smaller; for example when the number of nights without a blockage reached 50 (12th September), the probability became (10/60) to the power 6 =  0.1667 to the power 6 = 0.000021, that is 21 chances in a million or 1 in 47,619 (one million is the number that 0.000021 would have to be multiplied by to get 21).

Such probabilities as p = 0.0014 or p = 0.000021 do not predict the  frequency with which I can expect a blockage; neither do they predict the proportion of patients with a condition the same as mine having their blockages stopped.  All they mean is that in my case, it is almost certain that taking Nitrofurantoin and repositioning my catheter have reduced the chances of getting a blockage:  p = 0.000021 (the probability of there not being an association) or 1-p = 0.999979 (the probability of there being an association) are measures of the chance that Nitrofurantoin and catheter repositioning are associated with catheter blocking; they are not measures of what that association is, that is, how much they reduce the chances of a blockage. 

So for patients with a condition the same as mine, the treatment can be expected to reduce the frequency of blockages for almost all of them. 

It could be argued that although what has been calculated show a very strong correlation between taking Nitrofurantoin/catheter repositioning and the absence of blockages, demonstrating correlation is not the same as demonstrating cause: something else might have happened on 24th July 2016 when I started taking Nitrofurantoin regularly and it was this 'something else' which stopped my blockages.  This is true, but I am not aware of anything happening on that day or soon after, and which has continued to be effective since then, which could be this 'something else'.

It is possible to predict the number of blockages within any specified period using the Poisson probability distribution:

For example, suppose we wish to predict the chance of 1 blockage in a period of 7 days, the Poisson random variable would be 1.  The average rate of success is the average number of blockages which in the past have occurred in 7 days (number of blockages/number of days in observation period x 7). To predict the chance of 2 blockages in 28 days, the Poisson random variable would be 2 and the average rate of success would be the average number of blockages in 28 days.  As long as there are no blockages on nights following taking Nitrofurantoin, the average number of blockages for any period is 0: so until there is a blockage, the prediction of future blockages for any period is zero.

NITROFURANTOIN  AND  BLOCKAGES  16th January 2016 to 16th January 2017

My first blockage occurred on the night of 16/17th January 2016.

There were 23 blockages in the first 190 days, none in the following 176.
If Nitrofurantoin and catheter repositioning had no effect, the probability of having 23 blockages in 190 days followed by no blockage in 176 days is (190/(190+176)) to the power 23 or 0.5191 to the power 23 =  0.0000002823 which is less than 3 chances in 10 million (ten million is the number that 0.0000002823 would have to be multiplied by to get 2.823).
The base is 0.5191 and the exponent is 23.

The probability of Nitrofurantoin having had no effect is becoming even smaller every day I do not have a blockage.

The binomial distribution can also be used with the same result:

where N = 23, k = 23, p =0.5191 and the answer is p(k out of N)

The multinomial can be used too:
where the number of outcomes is 2 (night/day), the number of occurrences 23 and 0, p = 0.5191 and 1- 0.5191 = 0.4809.
....... continued as part 2


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Re: Preventing Urinary Catheter Blockages
« Reply #1 on: March 02, 2017, 04:58:09 AM »


Side-effects and build-up of bacterial resistance are concerns about antibiotics generally.  Although there are no indications that I have had either so far, I am now trying to determine the minimum effective dose of Nitrofurantoin. 

Having taken 50mg every day from 24th July until 22nd August (30 days), this was reduced to 3 or 4 times per week and then to just nights when I was feeling feverish as might warn of a urinary infection or when there was a considerable amount of sediment in my catheter:
August 24, 25, 26, 28, 29, 30;
September 1, 2, 4, 7, 8, 10, 13, 16, 18, 19, 22, 25;
October 1, 5, 6, 7, 11, 14, 15, 17, 20 (100mg), 21, 22, 23, 25, 29, 31;
November 4, 5, 7, 10, 13, 16, 19, 22, 24, 26, 28;
December 1, 3, 5, 8, 11, 12, 17, 22, 31;
January 8, 16, 18, 22;
February 5, 13, 16, 20, 25;


The Users' Information Leaflets issued by Dr Reddy's Laboratories and Genfura recommend 50 or 100mg four time per day for seven days for treatment of bacterial infections of the liver, bladder and other parts of the urinary tract and 50mg or 100mg once per day at night for the prevention of further infections but do not say for how long.  The connection between preventing infections and preventing catheter blockages is not mentioned.  The leaflets list many possible side-effects.  So far, I have not experienced any but others do; see for example:

Will it cease to be effective after a while?   So far it hasn't.  It has already provided me with a very welcome relief from the misery of regular catheter blockages, possibly prevented internal damage and saved a significant amount of nurses' time. 

Brumfitt and Hamilton-Miller support the use of Nitrofurantoin for long-term (12 months) prevention of urinary infections:; see also and


Has the catheter had any influence on the occurrence of blockages?  There is a widely-held view that catheter production has lagged a long way behind the technology available and is failing patients badly.  See for example:

I can refer only to the catheters I have had.  My indwelling suprapubic catheter was presented to me in hospital in May 2013 as being better than the intermittent urethral catheter used between January and May 2013.  This would have been impossible on returning home because I live alone and have very little movement in my hands.  The indwelling urinary catheter via the urethra was not mentioned to me, presumably because the hospital consultants thought it would be less suitable than the type I have got. 

In my case, my present type of catheter is the only practical one I was offered.  The threat of urinary infection is always with me.  Hot and cold sweats occur most days.  My arms are often stinging with cold while the rest of me, where I have sensation, is overheating.  It is possible that better catheters would render blockages something of the past, which would be welcome relief for more than 200,000 people in the UK with long-term catheters and several times as many when shorter-term users are included.

We may wonder why the enormous buying power of the NHS results in some not-very-good equipment and medications at high cost while in the commercial world, large organisations are able to use their buying power to secure what the customer wants at competitive prices.  An Internet search on NHS overcharged (1/2/17) revealed about 190,000 results for drugs:

and 143,000 for equipment:

The standard period between changes of catheter has been 12 weeks (5 weeks in hospital) but there have been some variations.  It was changed shortly before 11pm on 23/7/16 by a night nurse attending a blockage and was followed less than 4 hours later by a blockage of the new catheter, described by the nurse as 'positional'.  The catheter that was  replaced coincided with more blockages than any other I have had.  I had no further blockage with the new catheter which was replaced on 18/10/16.   In my case so far, there is no substantial evidence connecting blockages with particular catheters or with the period of time since installation  .....  but absence of evidence is not evidence of absence. 


Although Nitrofurantoin and catheter repositioning have eliminated blockages so far, often there is sediment in my catheter: so supporting methods are used to keep it clear:                             

1    High water intake: widely recommended to wash out loose sediment and to dilute urine and bacterial concentration: possibly a necessary but not sufficient method to prevent blockages.  It certainly did not cause the sudden cessation of blockages from 24/7/16.

2     Bladder wash-outs: I have never had a blockage on the night immediately following a wash-out but I have had at least one on the night after that: they reduce but do not eliminate blockages.

3    Loosening any sediment in the catheter by rolling it between the hands.

4    Adding vinegar to food seems to be followed by a clearer catheter (by lowering urine pH and acting as an antibiotic).  There are many other natural antibiotics which might help:

It looks possible that the sediment was caused by reducing the amount of Nitrofurantoin below 50mg per day and that the supporting methods might be alternatives to higher doses.   Nitrofurantoin does appear to clear sediment from the catheter not much longer than an hour after taking it - as would be expected from its property of preventing blockages.

It seems likely that the bacteria killed by Nitrofurantoin created the sediment which resulted in most of the blockages.  Samples of the contents of the catheter at the times of blockages would have been useful to test this.
Nitrofurantoin has been shown to be effective against: Citrobacter species, Coagulase negative staphylococci, E. coli, Enterococcus faecalis, Klebsiella species, Staphylococcus aureus, Staphylococcus saprophyticus, Streptococcus agalactiae
Observations point to one or more of these bacteria as the likely cause of perhaps three-quarters of my blockages (the other quarter being the result of physical obstructions).  A search of the Internet has not revealed any of them as being more likely than the others to have been the cause.  Without knowing which of these bacteria caused the blockages, we can not be sure that Nitrofurantoin is the most selective antibiotic to deal with them or what other antibiotics would also work.   Also, we do not know at what pH the blockages occurred.
Many or all strains of the following genera are resistant to Nitrofurantoin: Enterobacter, Klebsiella, Proteus, Pseudomonas


The methods explained in this paper will be effective only for blockages caused by certain types of bacteria or certain catheter positions.  It remains to be seen to what proportion of catheter blockages these conditions apply.  In July 2016, before taking Nitrofurantoin as part of this treatment, a rehabilitation consultant suggested to me that kidney stones might be the cause of my blockages.  Bits breaking off the stones would block the catheter.  In the absence of any samples from my catheter having been taken at the time of a blockage, this seemed a reasonable possibility, but now that the blockages have been demonstrated to be bacteriological (otherwise they would not have been stopped by Nitrofurantoin) it looks unlikely in my case - but not necessarily in others.

After reading an earlier version of this paper in November 2016, a urology consultant suggested to me that mine might be a case of bladder stones because these can cause re-infection.  Repeated infections, might in some cases, be prevented by removal of bladder stones.

The following are commonly mentioned symptoms of bladder stones, not necessarily soon after their formation:
1  lower abdominal pain,   2  pain or discomfort when urinating,   3  difficulty when starting or a stop-start in urinating,  4  cloudy or dark-coloured urine,  5  discomfort or pain in the penis,  6 urinating more frequently, especially at night,  7  blood in the urine.

Spinal injury and consequent loss of sensation  and use of a catheter might reduce awareness of some of these symptoms.   Cloudy urine is commonly mentioned but not sediment which would be needed to cause a catheter blockage.   Darkening of urine is also a usual consequence of  taking Nitrofurantoin.

Anyone with persistent catheter blockages might be recommended by their medical practitioner to have a cystoscopy, an examination of the bladder with a fine telescope, to detect whether there are any stones.  Stickler and Feneley suggest that Proteus mirabilis produced by bladder stones is a likely cause of catheter blockages:
However, Nitrofurantoin is not effective against most strains of Proteus.   See also

So Nitrofurantoin is unlikely to prevent blockages caused by bladder stones.


The nurses, particularly the night nurses, have left me with the impression that catheter blockages are much more common than they need to be.  Often, they left me with a cheery 'See you again soon'.  The prevailing attitude in both the medical and nursing professions that they are an inevitable consequence of having a catheter should be questioned. 

In November 2016 I 'phoned the night nurses to thank them for coming to unblock my catheter on 23 nights between January and July, to explain why I have not called them out since July, and to offer to send them a copy of this paper: 'We don't give out e-mail addresses over the phone'.
Meanwhile, patients wake in the early hours of the morning, sweating profusely, trembling with massive shocks of spasms, resulting in urine being forced back to the kidneys and in extreme cases, autonomic dysreflexia, internal damage and death. Night nurses rush between patients to unblock catheters which do not need to be blocked. Sometimes they have taken over 2 hours to reach me (although the average is about 1 hour 20 minutes), explaining that they have had a lot of patients with blocked catheters that night.
Recently, a nurse from the local health authority called to assess my condition. A friend who was with me mentioned my catheter blockages and offered her this paper: no thanks. 'It's something they can live with'.
Although I have not heard anyone else say so explicitly, 'something they can live with' reflects the prevailing attitude of others connected to the nursing and medical professions.  With a few exceptions, no-one wants to know and the few who do want to know are not in positions to persuade the medical and nursing professions to listen to a patient.
Such has been the resistance to an approved dose of an approved medication.  How much greater can we expect the difficulties of improvement in the medications available for spasms for example, or equipment such as catheters, when those needing them have been conditioned to expect nothing better than what they are given, when manufacturers are allowed to happily continue to sell the same old products.  I must say I am left wondering whether the brick wall of complacency about catheter blockages also applies to other treatments and equipment that those with spinal injuries need - including treating the injury itself - and beyond spinal injuries.

This, of course, is my own story.  My need for a catheter was caused by breaking my neck at C4/5 with consequent spinal damage and paralysis below my shoulders.  I do not know for how many others the treatment would be effective but I have no reason to believe that it  would not work for some of those - male or female - with catheters for other reasons.  Other people might need different doses of Nitrofurantoin.  If you have persistent blockages or know someone who has, do consider showing this paper to a medical practitioner. 

P.S. Still no blockage since the night of 23rd / 24th July.         

                                               2nd March 2017